Application Cases

Experiment Name: Study of Nonlinear Oscillatory Electroosmotic Flow at Insulating Walls Based on Laser-Induced Fluorescence Photobleaching Anemometry (LIFPA) Technology

Test Purpose: Laser-Induced Fluorescence Photobleaching Anemometry (LIFPA) is a novel micro/nanofluidic velocity measurement technology based on laser-induced fluorescence. LIFPA is developed based on the principles of Laser-Induced Fluorescence (LIF) and photobleaching. When a laser continuously irradiates a fluorescent material, the fluorescence intensity emitted by the material gradually weakens over time, a phenomenon known as photobleaching. When the concentration of the fluorescent material is constant, the longer the material is exposed to the laser, the stronger the photobleaching effect and the weaker the fluorescence intensity.

Testing Equipment: High-voltage amplifier, signal generator, laser, current preamplifier, etc.

Figure 1: Schematic diagram of the experimental system. (a) System diagram, including: (1) 405nm continuous laser; (2) AOM; (3) Spatial filter; (4) Lens; (5) Mirror; (6) Dichroic mirror; (7) Filter; (8) Multimode fiber; (9) Photon counter; (10) Current preamplifier and A/D converter; (11) Computer; (12) Syringe pump; (13) Mirror; (14) Objective lens; (15) Micrometer translation stage; (16) Nanometer translation stage. (b) Photograph of the system.

Experiment Process:

The LIFPA system used in the experiment is developed based on a confocal microscope system, as shown in Figure 1. The system uses a continuous laser with a wavelength of 405nm as the excitation light, with a maximum power of 500mW. At the output end of the laser, an acousto-optic modulator (AOM) is first used for beam modulation, with an aperture diameter of 2mm. Acousto-optic modulation is based on the acousto-optic effect, where the modulation signal is applied to the electroacoustic transducer in the form of an electrical signal (amplitude modulation), which is then converted into an ultrasonic field that changes in the form of an electrical signal. When a light wave passes through the acousto-optic medium, due to the acousto-optic interaction, the light wave undergoes diffraction, and the frequency, intensity, and direction of the diffracted light change with the ultrasonic field.

A solution is prepared, and then a rectangular microchannel is fabricated, with dimensions of 5mm in length, 300μm in width, and 100μm in height. The chip consists of three layers, processed and bonded layer by layer.

In the experiment, the oscillatory electroosmotic flow is generated by an applied alternating current (AC) electric field. Platinum wires are installed at both ends of the channel as electrodes. The AC electric field is generated by the signal generator and amplified by the high-voltage amplifier because the signal generator can only provide low-voltage and fixed-frequency AC signals, which do not meet the experimental requirements for higher voltage. Therefore, a high-voltage amplifier is used to enhance the signal. The signal generator can select the desired waveform, voltage, and frequency conditions according to experimental needs; the high-voltage amplifier can amplify the voltage at a fixed amplification ratio while keeping the waveform and electric field frequency unchanged. The amplification ratio is adjustable, and a 200-fold amplification is used here. Additionally, the high-voltage amplifier needs to be grounded to comply with laboratory rules and safety requirements.

Experimental Results:

LIFPA is a velocity measurement technology developed based on the relationship between fluorescence intensity and velocity, with high temporal and spatial resolution. By measuring the fluorescence intensity of the moving fluid, the velocity of the fluid can be calculated. For the overall system, a syringe pump can provide a stable fluid flow in the microchannel, and the high-voltage amplifier can provide a stable AC electric field within the microchannel, meeting the conditions required for measuring oscillatory electroosmotic flow.

Voltage Amplifier Recommendation: ATA-7015

Figure: Specification Parameters of the ATA-7015 High-Voltage Amplifier

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